1. Field of the Invention
This invention relates to the treatment of wooden articles and, in particular, it relates to methods useful for ablating at least a portion of the surface of wooden articles and thereby modifying the dimensions of the article's surface, and/or cleaning, embossing, or otherwise modifying the surface of wooden articles.
2. Description of the Art
The surfaces of a variety of wooden articles are often treated, either chemically or mechanically, to modify the article's dimensions, accentuate grain structure, emboss the surface or clean the article, prepare the surface for further use such as adhesion to another wooden article for the formation of composite structures such as laminates, furniture or other wooden structures, for finishing or coating with sealers, stains, paints, varnishes or other surface preparations, and a variety of other uses. Physical changes in the surfaces of wooden articles are usually achieved by mechanical means such as milling, planing, sandblasting or by the use of specialized machine or hand tools such as routers, lathes, and other specialized cutting implements. Certain chemical treatments such as treatment with strong mineral acids have also found limited application for the physical modification of the surface of wooden articles and for cleaning wooden articles to remove deposits and stains or to prepare the article surface for finishing or adhesion to another component. Stains, such as applied wood stains and chemical marks such as grease marks and the like, can be removed, to some extent, with stain removers and/or strong detergents. Surface discoloration such as that which results from the aging of redwood and cedar roofing and siding materials, can also be removed, to some extent, by chemical treatment.
Both the mechanical and chemical treating procedures which are currently employed to modify, clean and/or otherwise treat the surfaces of wooden articles suffer from certain limitations. For instance, mechanical procedures often cannot be employed to accomplish objectives that can be accomplished by chemical treatment such as cleaning a wooden surface to remove stains or to prepare the surface for finishing, gluing, etc. Furthermore, the use of mechanical woodworking unavoidably modifies the surface of the treated article in a manner characteristic of the working implement employed. Sandblasting is an effective procedure for cleaning some wooden surfaces such as exterior siding and roofing although it is cumbersome and expensive. While surfactants, solvents, and other cleaning agents are effective, to some extent, for cleaning wood surfaces or preparing such surfaces for further treatment, they are not adequate in many respects. For instance, many stains on wooden surfaces cannot be readily removed with surfactants or solvents. Such stains can be removed with strong mineral acids, such as sulfuric and nitric acids, but these materials are often undesirable due to their strong oxidizing and dehydrating activity which can mar and disfigure the wood surface.
Although combinations of urea and sulfuric acid are known, it has not been suggested that such combinations which contain the monourea adduct of sulfucic acid can be advantageously employed for treating wooden surfaces. For instance, D. F. du Toit, Verslag Akad. Wetenschappen, 22, 573-4 (abstracted in Chemical Abstracts, 8, 2346, 1914) disclosed that urea forms certain compounds with oxalic, acetic, hydrochloric, nitric and sulfuric acids. L. H. Dalman, "Ternary Systems of Urea and Acid. I. Urea, Nitric Acid and Water. II. Urea, Sulfuric Acid and Water. III. Urea, Oxalic Acid and Water"; JACS, 56, 549-53 (1934), disclosed the phase relationships between the solid phase and saturated solutions containing urea and sulfuric acid at 10.degree. C. and 25.degree. C. The Sulfur Institute, Sulfur Institute Bulletin No. 10 (1964), "Adding Plant Nutrient Sulfur to Fertilizer", disclosed that urea reacts with sulfuric acid to form two complexes of "urea sulfate" which are useful fertilizers. Methods of manufacturing certain combinations of urea and sulfuric acid are disclosed by Verdegaal et al. in U.S. Pat. No. 4,310,343 and by Jones in U.S. Pat. No. 4,116,664. However, neither these nor other investigators have recognized that urea-sulfuric acid compositions containing the monourea adduct of sulfuric acid are uniquely active toward the surfaces of wooden articles in a manner that renders their use particularly attractive for accomplishing various modifications of such wooden surfaces.
Accordingly, a need exists for improved processes for treating wooden surfaces, and particularly for improved processes for ablating the surface of wooden articles and for cleaning, milling, embossing, engraving, highlighting the grain structure, texturizing or shaping wooden articles and for improving the quality of wooden surfaces for subsequent treatment such as coating (painting, staining, etc.) and adhesion to form composite structures.
It is therefore a principal object of this invention to provide novel methods for treating the surface of wooden articles.
Another object of this invention is the provision of methods for ablating the surface of wooden articles.
Yet another object is the provision of methods for treating the surface of manufactured wooden articles.
Another object of this invention is the provision of methods for cleaning the surfaces of wooden articles.
Another object is the provision of methods for physically modifying the surface of wooden articles to emboss, engrave and/or texturize the surface and/or to highlight the grain structure of the wood surface.
Yet another object is the provision of methods for improving the surface quality of wooden articles prior to finishing, e.g., painting, staining, impregnation and the like.
Another object is a provision of methods for improving the surface of wooden articles prior to the adhesion of the treated wood surface to other substrates.
Other objects, aspects and advantages of this invention will be apparent to one skilled in the art in view of the following disclosure and the appended claims.